Treatment of microbial infection in host organisms requires an effective means to kill the microbe while doing as little harm to the host as possible. Accordingly, agents which target characteristics unique to a pathology-causing microorganism are desirable for treatment. Penicillin is an extremely well-known example of such an agent. Penicillin acts by inhibiting biosynthesis of bacterial cell walls. Since mammalian cells do not require cell walls for survival, administration of penicillin to a human infected with bacteria may kill the bacteria without killing human cells.
However, the use of antibiotics and antimicrobials has also resulted in increased resistance to these agents. As bacteria become resistant to older, more widely used antimicrobial agents, new antimicrobials must be developed in order to provide effective treatments for human and non-human animals suffering from microbial infection.
Peptidyl deformylase (PDF) is a metallopeptidase found in prokaryotic organisms, such as bacteria. Protein synthesis in prokaryotic organisms begins with N-formyl methionine (fMet). After initiation of protein synthesis, the formyl group is removed by the enzyme PDF; this activity is essential for maturation of proteins. It has been shown that PDF is required for bacterial growth (see Chang et al., J. Bacteriol., Vol.171, pp. 4071-4072 (1989); Meinnel et al., J. Bacteriol., Vol.176, No. 23, pp.7387-7390 (1994); Mazel et al., EMBO J., Vol. 13, No. 4, pp. 914-923 (1994)). Since protein synthesis in eukaryotic organisms does not depend on fMet for initiation, agents that will inhibit PDF are attractive candidates for development of new antimicrobial and antibacterial drugs. Prokaryotic organisms, including disease-causing prokaryotes, are described in Balows, Truper, Dworkin, Harder and Schleifer, Eds., The Prokaryotes, 2nd Ed., Springer-Verlag, NY (1992); and Holt, Editor-in-Chief, Bergey's Manual of Systematic Bacteriology, Vols. 1-4, Williams & Wilkins, Baltimore (1982, 1986, 1989).
PDF is part of the metalloproteinase superfamily. While PDF clearly shares many of the features which characterize metalloproteinases, it differs from other members of the superfamily in several important respects. First, the metal ion in the active enzyme appears to be Fe (II), or possibly another divalent cationic metal, instead of the zinc ion more commonly encountered (see Rajagopalan et al., J. Am. Chem. Soc., Vol. 119, pp. 12418-12419 (1997)). Second, the divalent ion appears to play an important role, not only in catalysis, but also in the structural integrity of the protein. Third, the third ligand of the divalent ion is a cysteine, rather than a histidine or a glutamate, as in other metalloproteinases and is not located at the C-terminal side of the HEXXH motif but far away along the amino acid sequence and N-terminal to the motif. Finally, the solution structure shows significant differences in the secondary and tertiary structure of PDF compared to other prototypical metalloproteinases (see Meinnel et al., J. Mol. Biol., Vol. 262, pp. 375-386 (1996)). PDF from E. coli, Bacillus stearothermophilus and Thermus thermophilus have been characterized (see Meinnel et al., J. Mol. Biol., Vol. 267, pp. 749-761 (1997)). The enzyme studied by Meinnel et al. contained a zinc ion as the divalent ion and the structural features summarized above were obtained from zinc-containing proteins. The structure of the protein has also been determined by NMR (see O'Connell et al., J. Biomol., NMR, Vol. 13, No. 4, pp. 311-324 (1999)).
Metalloproteinases are critical to many aspects of normal metabolism. The class known as matrix metalloproteinases (MMPs) are involved in tissue remodeling, such as degradation of the extracellular matrix. These enzymes are believed to play a role in normal or beneficial biological events, such as the formation of the corpus luteum during pregnancy (see Liu et al., Endocrinology, Vol. 140, No. 11, pp. 5330-5338 (1999)), wound healing (see Yamagiwa et al., Bone, Vol. 25, No. 2, pp. 197-203 (1999)), and bone growth in healthy children (see Bord et al., Bone, Vol. 23, No. 1, pp. 7-12 (1998)). Disorders involving metalloproteinases have been implicated in several diseases such as cancer, arthritis and autoimmune diseases.
Because of the importance of MMPs in normal physiological processes, it would be preferable to develop agents that inhibit PDF, a metalloproteinase present only in prokaryotes, while avoiding significant inhibition of MMPs. Alternatively, PDF inhibitors which also inhibit MMPs may be of use where the therapeutic benefits of inhibiting PDF outweigh the risk of side effects from MMP inhibition.
A wide variety of compounds have been developed as candidate inhibitors of MMPs and other metalloproteinases, and much effort has also been directed at synthetic methods for these compounds and related compounds (see Izquierdo-Martin et al., J. Am. Chem. Soc., Vol. 114, pp. 325-331 (1992); Cushman et al., Chapter 5, “Specific Inhibitors of Zinc Metallopeptidases”, Topics in Molecular Pharmacology, Burgen & Roberts, Eds. (1981); Mohler et al., Nature, Vol. 370, pp. 218-220 (1994); Gearing et al., Nature, Vol. 370, pp. 555-557 (1994); McGeehan et al., Nature, Vol. 370, pp. 558-561 (1994); U.S. Pat. Nos. 4,052,511, 4,303,662, 4,311,705, 4,321,383, 4,599,361, 4,804,676, 5,128,346, 5,256,657, 5,268,384, 5,447,929, 5,453,423, 5,552,419, 5,614,625, 5,643,908, 5,712,300 and 5,869,518; European patent publications EP 236872, EP 274453, EP 334244, EP 423943, EP 489577, EP 489579, EP 497192, EP 574758; and International PCT Patent Applications Publication Nos. WO 90/05716, WO 90/05719, WO 91/02716, WO 92/13831, WO 92/22523, WO 93/09090, WO 93/09097, WO 93/20047, WO 93/24449, WO 93/24475, WO 94/02446, WO 94/02447, WO 94/21612, WO 94/25434, WO 94/25435, WO 95/33731, WO 96/25156, WO 96/26918 WO 97/30707, WO 97/49674, WO 98/55449 and WO 99/02510.
Research on inhibitors of PDF is much less extensive than that for inhibitors of MMPs. N-formyl hydroxylamine derivatives are described in International Patent Application WO 99/39704. Peptide aldehyde inhibitors of PDFs are described in Durand et al., Arch. Biochem. Biophys., Vol. 367, No. 2, pp. 297-302 (1999). The PDF inhibitor (S)-2-O-(H-phosphonoxy)-L-caproyl-L-leucyl-p-nitroanilide is described in Hao et al., Biochem., Vol. 38, pp. 4712-4719 (1999), and peptidyl H-phosphonate inhibitors of PDF are discussed in Hu et al., Bioorg. Med. Chem. Lett., Vol. 8, pp. 2479-2482 (1998). Formylated peptides and pseudopeptides are described in Meinnel et al., Biochem., Vol. 38, No. 1, pp. 4288-4295 (1999) as inhibitors of PDF.
In view of the importance of identifying new antibiotics to treat bacteria resistant to existing antibiotics, and the relatively small amount of work that has been carried out on PDF inhibitors, it is desirable to develop novel inhibitors of PDF for evaluation and use as antibacterial and antimicrobial agents. The present invention fulfills this need.